Catalytic reforming process to obtain naphthalenes



J. C. STRICKLAND Filed Nov. 22, 1956 July 23, 1968 CATALYTIC HEFORMINGPROCESS To OBTAIN NAPHTHALENES 3,394,073 Patented July 23, 19683,394,073 CATALYTHC REFGRMllNG PROCESS Tt) OBTAIN NAPHTHALENES .lohn C.Strickland, Houston, Tex., assigner' to Texaco Inc., New York, NY., acorporation of Delaware Filed Nov. 22, 1966, Ser. No. 596,323 5 Claims.(Cl. 20S- 65) ABSTRACT 0F THE DSCLUSURE This invention relates to ahydrocarbon conversion process and more particularly to a method ofreforming gasoline boiling range hydrocarbons and enriching the aromaticcontent of kerosene boiling range hydrocarbons. In accordance with theprocess of the invention, gasoline boiling range hydrocarbons arecontacted with a reforming catalyst at reforming conditions in aninitial conversion zone, kerosene boiling range hydrocarbons arecombined with the efliuent of said initial conversion zone and theresulting adrnixture contacted with a reforming catalyst at reformingconditions in a terminal conversion zone, and reformed gasoline boilingrange hydrocarbon product and naphthalene and alkyl naphthalene productare separated from the efliuent of said terminal conversion zone.

Detailed description of the invention The expanding demand fornaphthalene has outpaced the supply from usual sources and created ademand for increased production from petroleum sources. In order toproduce the maximum amount of naphthalene, it is not only necessary toseparate the naphthalene present in petroleum streams per se, but it hasbeen found necessary to prepare naphthalene by the conversion of otherhydrocarbons, for example, by the dehydroaromatization of decalin andtetralin and by the hydrodealkylation of alkyl naphthalenes. Catalyticreforming employing catalysts containing platinum group metals is widelyused in the petroleum industry as a means of producing aromatics and toimprove the anti-knock characteristics of gasoline fractions. Inreforming gasoline, cycloparains are dehydrogenated to producearomatics, straight chain hydrocarbons are isomerized to form morehighly branched hydrocarbons and parafnic hydrocarbons are cyclicized toform aromatic compounds. Other reactions including hydrogen transfer andselective cracking contribute to the improved anti-knock characteristicsof the reformed product. In conventional catalytic reforming forgasoline production the charge stock usually has an end point less than400 F., for example, about 380 F., so that the reformate product may beincluded in gasoline without rerunning to gasoline end pointspecifications. However, charge stocks having components boiling aboveabout 400 F. and up to about 425 F. end point may be included in thefeed for conversion of these components to fractions boiling below about400 F. for ultimate inclusion in gasoline but in this case it is usuallynecessary to employ rerunning to remove the resulting high end pointtail which is undesirable in gasoline blends.

When catalytically reforming high end point gasoline feed stocks, thedistillation bottoms from rerunning the catalytic reformate is rich innaphthalene and alkyl naphthalenes. However, the inclusion of largeamount of high end point material in the feed to catalytic reforming isundesirable since the inclusion of such material correspondingly reducesthe amount of gasoline produced, which gasoline is the primary product.Additionally, the higher end point material limits the severity whichmay be applied to the gasoline feed stock Without encounteringaccelerated deactivation of the catalyst..

In the catalytic reforming of gasoline fractions, a domihating reactionis the dehydrogenation of naphthenes to aromatics. This reaction ishighly endothermic. In order to maintain high conversion, it isnecessary to maintain the reaction temperature at a level of about 875to 1000 F. It is customary therefore to divide the catalytic reactionzone into a plurality of individual reactors with reheat of the reactionmixture between reactors. The dehydrogenation reaction proceeds rapidly`and is largely completed in the rst two 0r three reactors. In a typicalcatalytic reforming system, the catalyst is divided into four reactors.Since most of the dehydrogenation occurs in the early stages, re-heat isrequired more frequently and the initial reactor vessels are smallerthan the nal catalytic reforming reactor vessel. In the linal reactor,the principal reaction is hydrocracking yand hydroisomerization.Typically, about 40 percent of the catalyst in the system is placed inthe last reactor.

It has been found that a 430 F. end point fraction of a straight-runkerosene, which is rich in materials which can be converted bydehydroaromatization to naphthalene and alkylnaphthalenes may beincluded in the feed of a catalytic reforming unit to producenaphthalene and alkylnaphthalenes. Alkylnaphthalenes are readilyconverted to naphthalene by hydrodealkylation and are frequentlyreferred to as naphthalene precursors. The 430 F. end point fractionseparated from kerosene typically has an initial boiling point withinthe range of about 275 to 375 F., a 50% point within the range of about360 to 410 F. and `an end point of 420 to 440 F. and contains labout 35to 85 volume percent of cycloparalns, dicycloparains and aromatics.However, when such a stock is included in the feed to the rst reactor ofa catalytic reforming unit for conversion to naphthalene Aandnaphthalene precursors, it is necessary to reduce the amount of gasolinecharged to maintain the same elfective space velocity needed to maintainthe quality of the reformed gasoline. Such operation results in anundesirable reduction in the production of reformed gasoline. I havefound that this disadvantage may be avoided and an unexpectedly highyield of naphthalene and naphthalene precursors can be produced byintroducing a 430 F. end point kerosene fraction into the feed to thelast reactor of a series of catalytic reforming reactors. In this waythe last reactor effects dehydrogenation of the naphthalene precursorsof the kerosene cut Without interfering or diminishing the hydrocrackingof the gasoline being treated therein. At the Isame time, a higher yieldof naphthalene precursors is obtained than is obtained by inclusion ofthe same amount of high boiling material in the feed to the primaryreaction zone.

In accordance with the process of this invention a gasoline boilingrange hydrocarbon is contracted with a reforming catalyst comprising aplatinum group metal on alumina. containing combined halogen in aninitial reformassauts ing zone at a space velocity within the range ofabout l to 7 volumes of charge per hour per volume of catalyst.Reforming temperatures within the range of about 875 to 1000 F. andpressures within the range of about 200 to 800 pounds per square inchgauge are employed. Hydrogen is supplied to the reaction zone as recyclegas at a rate within the range of about 4 to 15 mols of hydrogen to eachmol of hydrocarbon charged. Although the initial conversion zone may bea single reactor, it is usually made up of two or three reactors withassociated preheater and reheaters in which case the reformingconditions stated apply to the reactors taken as a group. The partiallyreformed gasoline is then passed in admixture with a 430 F. end pointkerosene fraction to a terminal reaction zone which again may be one ormore reactors, but usually comprises a single reactor. The reformingconditions ernployed in the terminal reaction zone include a spacevelocity within the range of about 3 to 35, a temperature within therange of about 875 to 1000 F., a pressure within the range of about 200to 800 pounds per square inch gauge and a hydrogen to hydrocarbon molratio of about 2 to 15. The amount of 430 F. kerosene fraction injectedinto the terminal reaction Zone is usually within the range of about 10to 100 volume percent of the gasoline feed to the initial conversionzone. Conveniently, the amount of 430 F. end point kerosene employed isthe normal ratio of production of the kerosene fraction to straight rungasoline feed which typically may be about 55% of the straight rungasoline feed.

The invention will be further described in conjunction with thefollowing drawing, tests and examples. Although the drawing illustratesone form of apparatus in which the invention may be practiced, it is notintended to limit the invention to the particular apparatus or materialsdescribed. The drawing is a schematic liow diagram and for clarity omitsauxiliary equipment such as pumps, compression controls, heat exchangemeans which are well known and form no part of the present invention.

Referring to the figure, catalytic reforming feed in line 1, typicallyhaving an initial boiling point of about 200 to 240 F. and an end pointwithin the range of about 380 to 400 F. and recycle hydrogen from line 4comprising about 80 to 95 percent hydrogen are admixed and passedthrough coil 2 in heater 3. In heating coil 2, the gasolinehydrogenmixture is heated to a temperature of about 950 F. and passed throughline 6 to reactor 7. Reactor 7 contains a bed of solid reformingcatalyst such as the well-known Platforming catalyst. As the reactantspass through reactor 7, the endothermic heat of reaction causes thetemperature to drop so that the effluent is discharged at a temperatureof about 840 F. Effluent in line 8 is passed through coil 9 in heater 10to reheat the hydrocarbon-hydrogen mixture to a temperature of about 945F. The reheated mixture from coil 9 is passed through line 12 to reactor13. Again, the heat of reaction causes the temperature to drop so thatthe efiiuent of reactor 13 is discharged through line 14'- at atemperature of about 900 F. The hydrogen-hydrocarbon mixture is thenpassed through heating coil 15 in heater 17 where the temperature israised to about 940 F. The heated mixture at a temperature of 940 F. ispassed through line 18 to reactor 20. Again, the heat of reaction causesa temperature drop to about 930 F. Effluent from reactor 20 at 930 F. inline 21 is combined with a 430 F. end point cut of kerosene from line 22and the mixture passed to heating coil 23 in heater 24. In heater 24,the reactants are heated to a temperature of about 940 F. and passedthrough line ZS to the terminal reactor 26. ln the terminal reactor 26hydrocracking of the gasoline is effected and, at the same time,dehydroaromatization of the high boiling bicyclonaphthenes proceeds toform naphthalene and naphthalene precursors. The efliuent from reactor26 is discharged through line 27, cooler 28 and line 29 to separator 30.Vapor and liquid phases separate in separator 30 and recycle gas iswithdrawn and passed through line 4 to the feed line 1. Separated liquidis withdrawn through line 31 and passed to stabilizer 32. In stabilizer32, low boiling hydrocarbons such as butanes and lighter are strippedfrom the liquid product and discharged through line 34. Stabilizedliquid is withdrawn through line 33 and passed to rerun tower 35 wherethe liquid product is separated into reformed gasoline which is removedas distillate through line 36 and distillation bottoms comprisingnaphthalene and naphthalene precursors which are withdrawn through line37.

EXAMPLE The effectiveness of the method of this invention of introducinga 430 F. end point kerosene cut into the terminal zone of amulti-reactor catalytic reforming system is shown in the followingcomparison with conventional catalytic reforming of straight rungasoline, and catalytic reforming of straight run gasoline withintroduction of a 430 F. end point cut of gasoline into the initial zoneof the same catalytic reforming system. In the tests, a conventionalcatalytic platinum-alumina-combined halogen reforming catalystidentified as UOP R-S catalyst is used in a four-reactor system. Each ofthe first three reactors contains 20 percent of the total catalyst andthe terminal reactor contains 40 percent of the total catalyst. Feedstocks having the following tests are employed:

Four tests are made at; the conditions given below and with the resultsshown in Table I.

Test A shows the small amount of naphthalene and naphthalene precursorproduced in conventional catalytic reforming operation employing astraight run gasoline feed. In comparison, Test B shows the amount ofnaphthalene and naphthalene precursor produced when operating with thesame total amount of a mixed feed stock comprising 64.0 percent straightrun gasoline and 36 percent of a 430 F. end point fraction of kerosene.Under these conditions, the space velocity and hydrogen to hydrocarbonmol ratio are maintained the same in Test B as in Test A whereby thegasoline component of the feed is subjected to the same severity. Itwill be recognized that although this method of operation substantiallyincreases the yield of naphthalene and naphthalene precursors, itsubstantially reduces the amount of gasoline charged and hence theamount of catalytic reformate produced. Test C shows the effect ofincreasing the total feed rate of a mixed gasoline-kerosene feed to theextent that the feed contains the same amount of gasoline as employed inTest A. This increased throughput results in a higher space velocityand, accordingly, less severe gasoline reforming conditions, butproduces an increased yield of naphthalene and naphthalene precursors.Test D illustrates the present invention wherein gasoline is charged t0the initial reforming zone comprising three reactors at substantiallythe same rate as employed in Test A, a 430 F. EP kerosene cut isintroduced with the effluent of the third reactor, and the mixturepassed as feed to the fourth reactor. The yield of 40.55 cc. per hour 0fnaphthalene and naphthalene precursors is higher in Test D than in anyof the other tests and, surprisingly, is substantially higher than inTest C wherein the same amount of feed is employed but with all feedpassed to the first reactor.

TABLE I Test A Test B All feed to first reaetor All iced to firstreactor. Feed 680 cc.lhr. of SR gasoline 432 cc./hr. of SR gasoline plus248 ce./hr. of 430 F. EP kerosene cut.

Conditions:

Reactor Temperature:

No, 1 970 97() N0. 2-- 970 970 No. 3- 970 970 No. 4.. 070 970 Pressure,p.s i.g 50u 500 H drogen Recycle Rate, Moles H2 per mol iced:

Basis 4 reactors 3 8.3 8. 3 Basis reactors 1-3 3 8. 3 8. 3 Basis reactor4 4.. 8. 3 8. 3 Space Velocity, v./lir./v

Basis 4 reactors 1 3. 0 3. 0 Basis reactors 1-3 1 5i 0 5. 0 Basisreactor 4 2 7. 5 7. 5 NapthaleneNapthalene Precursor' Yield, cc./hr. 8.9 23. 5

Test C Test D Flow All feed to first reactor Gasoline to first reactor,

430 F. El? kerosene added to feed to fourth reactor. Feed 675 cc./hr. ofSR gasoline 675 ce./hr. of SR gasoline to plus 375 cc./hr. of 430 F.

EP kerosene cut.

first reactor, plus 375 cc.ll1r. of 430 I". El kerosehe cut to fourthreactor.

Conditions:

Reactor Temperature:

No. 1 97o No. 2 97o No. 3 97o No. 4-- 97o Pressure, p. 500 HydrogenRecycle Basis 4 reactors L. 5 7

Basis reactors 1-3 3, Basis reactor 4 4. Space Velocity, v/hr./v.

Basis 4 reactors 1..... Basis reactors 1-3 1 Basis reactor 4 2Napllithalene-Naphthalene Precursor Yield,

ce. hr

1 Calculated on the basis ofthe volume of liquid feed charged to thefirst reactor. 2 Calculated on the basis oi the volume of liquid feedcharged to the first reactor plus, in Test D, the volume of additionalliquie charged to the fourth reactor.

3 Calculated on the basis oi the mols of liquid charged to the firstreactor.

4 Calculated on the basis of the mois of liquid charged to the firstreactor plus the number of mois of additional liquid charged to thefourth reactor.

I claim:

1. In a process Iwherein a gasoline boiling range hydro carbon iscontacted with a platinum group metal reforming catalyst at reformingconditions in a plurality of reforming zones in series, the method ofconcomitantly preparing a naphthalene precursor feed stock whichcomprises introducing a straight run kerosene fraction having an initialboiling point within the range of about 275 to 375 F., a 50% pointwithin the range of about 360 to 410 F. and an end point of 420 to 440F. and containing about to 85 volume percent of cycloparaflins,dicycloparains and aromatics intermediate to at least two of saidplurality of reforming zones and separating reformed gasoline andnaphthalene precusor feed stock from the effluent of the ylast of saidplurality of reforming zones.

2. The method of reforming gasoline boiling range hydrocarbons andenriching the aromatic content of a straight run kerosene fractionvhaving an initial boiling point within the range of about 275 to 375F., a 50% point within the range of about 360 to 410 F. and an endlpoint of 420 to 440 F. and containing about 35 to 85 volume percent ofcycloparaffns, dicycloparaflins and aromatics which comprises,

passing said gasoline boiling range hydrocarbons to the first of atleasttwo separate catalytic reforming zones in series flow in contact with aplatinum group metal reforming catalyst under catalytic reformingconditions,

passing said straight run kerosene fraction to one of said catalyticreforming zones subsequent to the catalytic reforming zone to which saidgasoline boiling range hydrocarbons are passed whereby partiallyreformed gasoline and said kerosene fraction are subjected to catalyticreforming conditions in said subsequent reforming zone,

withdrawing effluent .from said subsequent reforming zone and separatingtherefrom a gasoline fraction and a fraction comprising naphthalene andalkyl na-phthalenes.

3. A method of reforming gasoline boiling range hydrocarbons andconcomitantly forming a hydrocarbon stock rich in naphthalene and alkylnaphthalenes which comprises contacting said gasoline boiling rangehydrocarbons and hydrogen with a platinum group metal reforming catalystat reforming conditions in an initial conversion zone,

withdrawing effluent from said initial conversion zone,

admixing a straight run kerosene fraction having an initial boilingpoint within the range of about 275 to 375 F., a 50% point within therange of about 360 to 410 F. and an end point of 420 to 440 F. andcontaining about 35 to 85 volume percent of cycloparaiiins,dicycloparaiiins and aromatics with said eiuent from said initialconversion zone and contacting the resulting `mixture with a reformingcatalyst at reforming conditions in a terminal conversion zone,

withdrawing effluent from said terminal conversion zone and separatingtherefrom a first product fraction comprising reformed gasoline boilingrange hydrocarbons and a second product fraction comprising nephthaleneand alkyl naphthalenes.

4. The method of claim 3 wherein said gasoline boiling rangehydrocarbons are contacted with a catalyst comprising a platinum groupmetal reforming catalyst at a space velocity within the range of about 1to 7 volumes of charge per hour per volume of catalyst, a temperaturewithin the lrange of about 875 to 10UO F., a pressure Within the rangeof about 200 to 800 pounds per square inch gauge, and a hydrogen recyclerate within the range of about 4 to 15 mols of hydrogen per mol ofhydrocarbon charged to said initial conversion zone and said partiallyreformed gasoline boiling range hydrocarbons and said kerosene boilingrange hydrocarbons are contacted with a platinum group metal reformingcatalyst at a space velocity within the range of about 3 to 35, atemperature within the range of about 875 to 1000 F., a pressure withinthe range of about 200 to 800 pounds per square inch gauge, and ahydrogen recycle rate within the range of about 2 to 15 mols hydrogenper mol of hydrocarbons.

References Cited UNITED STATES PATENTS 7/1957 Hengstebeck 20s-65 11/1960Friedman 26o66s DELBERT E. GANTZ, Primary Examiner.

A. RIMENS, Assistant Examiner.

